The present invention relates to improvements in electrolytic cells with vertical electrodes, more particularly in cells furnished with metal anodes and intended for the production of alkali metal chlorate or hypochlorite or the production of chlorine.
It is known to employ metal anodes in cells electrolysing aqueous solutions of alkali metal halide. These anodes, for example, consist of plates of platinum or of plates of a film-forming metal such as titanium covered with an active coating comprising a metal or a compound of a metal of the platinum group. These metal anodes also sometimes contain a core of a metal that is cheaper and has a better electrical conductivity, such as copper or aluminium.
Until now, the development of cells with metal anodes has been relatively slow, because of the difficulties encountered in fixing these anodes inside the cell and connecting them to a current lead. Various solutions have been proposed to resolve these difficulties, but none of them seem to have given full satisfaction up to now.
In British Patent Specification No. 1,125,493 of Imperial Metal Industries (Kynoch) Limited it is proposed, for example, to fix the anodes by bolting, riveting or welding on to a titanium plate which forms the base of the cell and is anchored on a concrete foundation. The current is led to the anodes by bars of copper or aluminium, embedded in the concrete foundation and welded to the lower face of the titanium plate vertically beneath the anodes.
The construction of an anode assembly of this type is costly and difficult. It necessitates firm anchorage of the titanium plate on the concrete foundation, in order to prevent the plate from deforming and causing a lateral displacement of the anodes during operation of the cell.
This known anode assembly has the further disadvantage that is entails significant energy losses through the Joule effect, owing to passage of the current from the current leads to the anodes through the titanium sheet of low electrical conductivity.
It has also been proposed, in Belgium Pat. No. 739420, to mount the metal anodes on vertical anode supports and to support the latter on a rigid metallic foundation, which is covered by a protective insulating layer and forms the base of the cell. The rigid metallic foundation may, for example, be made of copper or aluminium and may then serve also as the current lead to the anodes, or alternatively current leads may be suspended beneath the foundation from extensions of the anode support.
This known anode assembly has the double disadvantage of being heavy and costly, because of the great thickness necessary in the metallic foundation in order to ensure that it has sufficient rigidity.
Furthermore, during operation of the cell, the large sized metallic foundation is inevitably the seat of a gradient of internal stresses of thermal origin, which can lead to its deformation and to a lateral displacement of the anodes in the cell.